Method for indicating power-consumption status

ABSTRACT

A method and apparatus for improved indication of power-consumption status in a computer system is described. The computer system includes a light-emitting diode (LED) which produces an optical signal. The apparent intensity of the optical signal is controlled by a pulsed LED control signal having an adjustable duty cycle. By varying the duty cycle, the apparent intensity of the optical signal is varied. The rate at which the duty cycle is varied may be selected to produce an apparent intensity optical signal which varies continuously between a greatest and a least intensity. Also, the rate at which the duty cycle is varied may be selected from a plurality of rates, each corresponding with a one of a plurality of power-consumption states in which the computer system can operate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.08/779,578, filed Jan. 7, 1997.

TECHNICAL FIELD

The present invention relates generally to a method for providingpower-consumption status information in a computer system, and moreparticularly, to a method for providing optical signals to a userindicating the power-consumption status of the computer system.

BACKGROUND OF THE INVENTION

The use of computers, especially personal computers (PCs) is widespread.A PC includes a number of individual components, such as amicroprocessor, memory modules, various system and bus control units,and a wide variety of data input/output (I/O) devices. The componentsincluded in a PC require electrical power for operation, and asignificant amount of energy is wasted when the PC is not used whilemaintained in a powered-up state. This is particularly disadvantageousfor portable notebook computers, which rely on batteries for power. Inorder to provide more energy-efficient PCs, power management techniquesand circuitry have been developed which place the PC into one or morepowered-down states at appropriate times. For example, a PC cansuccessively enter states or modes of progressively lower powerconsumption until a user interaction or other selected event occurs.Typical portable computers have states such as Full-On, Standby,Suspend, and Off.

Many portable computers include an optical status indicator with alight-emitting diode (LED) to indicate a current power-consumptionstatus. Typically, the LED provides a constant intensity optical signal(as seen by the user) when the computer is in a Full-On state, and theLED emits no light when the computer is Off. When the computer isoperating in one of the powered-down states, such as Standby or Suspend,the LED flashes off and on. The flashing LED can be aestheticallyirritating to some users, and does not provide information indicating inwhich of the various powered-down states the computer currentlyoperates.

SUMMARY OF THE INVENTION

The present invention is embodied in a method and apparatus for improvedindication of power-consumption status in a computer system. A computersystem includes a processor coupled with a system controller whichoperates to place the processor in a plurality of powered-down states. Asystem status indicator produces a plurality of system status outputsignals, each corresponding with a respective one of the powered-downstates.

In one embodiment, the system status indicator includes an opticalstatus indicator which produces an optical status output signal. Whenthe system is in a powered-down state, the optical status output signalhas a modulated apparent intensity and appears to gradually vary betweena greatest and a least intensity. The modulation frequency may beselected to correspond with a respective one of the powered-down states,thereby providing a user with information regarding in which of thevarious powered-down states the computer system currently operates.

A method is provided for operating a computer system having alight-emitting diode to provide optical power-consumption statusinformation. A duty cycle value is selected, and a pulsed electriccurrent having the selected duty cycle is applied to the light-emittingdiode. The duty cycle is then modified, and a pulsed electric currenthaving the modified duty cycle is then applied to the light-emittingdiode. In this way, the apparent intensity of the optical signalproduced by the light-emitting diode is varied. The pulsed electriccurrent having the selected duty cycle is applied for a selected timeinterval prior to modifying the duty cycle value. By choosing from oneof a plurality of values for the selected time interval, the frequencyof variation in optical signal intensity is adjusted accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a preferred embodiment of acomputer system having a power-consumption status indicator according tothe present invention.

FIG. 2 is a functional block diagram of a preferred embodiment of thepower-consumption status indicator of FIG. 1, and includes an LED drivercircuit.

FIG. 3 is a functional block diagram of a first embodiment of the LEDdriver circuit of FIG. 2.

FIG. 4 is a flowchart of a software routine executed by amicrocontroller included in the LED driver circuit of FIG. 3.

FIG. 5 is a functional block diagram of a second and preferredembodiment of the LED driver circuit of FIG. 2.

FIG. 6 is a flowchart of a software subroutine executed by amicrocontroller included in the LED driver circuit of FIG. 5.

FIG. 7 is a functional block diagram of a third embodiment of the LEDdriver circuit of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

In the following, a novel computer system and method is described withcertain specific details set forth in order to provide a sufficientunderstanding of various embodiments of the present invention. However,one skilled in the art will understand that the present invention may bepracticed without these details. In other instances, well-knowncircuits, control signals, timing protocols, and software operations arenot described in detail in order not to unnecessarily obscure thedescription of the embodiments of the invention.

FIG. 1 shows a preferred embodiment of a computer system 10, such as anIBM-compatible PC, according to the present invention. A microprocessor12, such as a Pentium® processor, is connected to a processor bus 14which carries address, data, and control signals. The processor bus 14is in turn connected to a system controller 16, such as a Picopower™Vesuvius V1-LS controller. The processor bus 14 is also connected to acache memory 18, such as a static random access memory (SRAM) modulemanufactured by Micron Technology, Inc. The system controller 16 acts asa memory controller accessing a main memory, such as a system dynamicrandom access memory (DRAM) 20, via a memory address and control bus 22.A data portion of the processor bus 14 is coupled with the system DRAM20 by a memory data bus 24. The system DRAM 20 can include any ofvarious known memory devices, such as DRAM devices manufactured byMicron Technology, Inc. Other functions included in the systemcontroller 16, which may or may not be integrated on a single chip,include reset and clock interface circuitry, cache controller circuitry,memory data path control circuitry, system interrupt control circuitry,and general processor bus and I/O bus interface circuitry.

The system controller 16 also functions as a bridge circuit between theprocessor bus 14 and a system bus, such as I/O bus 26. The I/O bus 26may itself be a combination of one or more bus systems with associatedinterface circuitry (e.g., PCI bus with connected SCSI and ISA bussystems). One or more data input devices are coupled with the I/O bus26, such as a keyboard 27 and pointing device 28 with a keyboard/mousecontroller 29. Also, one or more data output devices are coupled withthe I/O bus 26, such as a video display unit 30 with VGA controller 31,and a printer 32 with printer port adapter 33. Additionally, one or moredata storage devices 34 and associated controller(s) 35 are coupled withthe I/O bus 26. Well-known examples include a floppy disk drive with DMAcontroller, a hard disk drive with EIDE controller, and a CD-ROM drivewith SCSI controller. Further connected to the I/O bus 26 are expansionslots 37 to provide future accommodation of other I/O devices notselected during the original design of the computer system.

The system controller 16 includes a power management controller 36having a plurality of programmable timing registers 38 associated with aplurality of system mode timers 40. The timing registers 38 areprogrammed during initialization of the computer system with values thatcontrol the expiration of the system mode timers 40. In response to theexpiration of one of the system mode timers 40, the power managementcontroller 36 causes the microprocessor 12 to be placed in acorresponding state or mode of lower power consumption. For example, themicroprocessor 12 might be placed in a Standby mode after five minutesof system inactivity, and in a Suspend mode after 15 minutes of suchinactivity. Those skilled in the art understand that even inpowered-down modes, the microprocessor 12 continues to processinstructions associated with low level system activity, such as timertick events. The computer system 10 is referred to as inactive evenwhile the microprocessor 12 processes such low level system activity.

A system status indicator 42 is coupled with the I/O bus 26 and producesstatus output signals 43 to a user of the computer system 10 to indicatein which of the various power-consumption states the computer system isoperating. The preferred embodiment of the system status indicator 42produces status output signals 43 which are optical signals. Forexample, LEDs can be employed to provide optical information to acomputer user.

FIG. 2 shows certain details of a preferred embodiment of the systemstatus indicator 42. The system status indicator 42 includes an LEDdriver circuit 44 which gates current through an LED 46 by applying anLED control signal to the control terminal of an electronicallycontrolled switch, such as a transistor 48. To protect the LED 46, acurrent limiting resistor 50 is included. In accordance with the presentinvention, the LED control signal is modulated (as described below) toprovide a variable intensity optical output signal from the LED 46. Inplace of the unaesthetic blinking of an LED, as in prior art systems,the apparent intensity of the LED 46 may be gradually increased anddecreased to indicate operation of the computer system 10 in apowered-down state. The rate at which the apparent intensity varies canbe adjusted in correspondence with the various powered-down states inwhich the computer system 10 operates.

Those skilled in the art will appreciate a number of advantages providedby the system status indicator 42 of the computer system 10. Oneadvantage is an aesthetic one, in which users of the computer system 10will view the LED 46 as having an apparent intensity which variesapproximately continuously between a highest intensity and a lowestintensity. This is not as distracting to the eye as currently availablecomputer systems in which the LED blinks or flashes. Further, most oftoday's PCs include a number of powered-down states which are enteredafter successively longer time intervals of system inactivity. Thesystem status indicator 42 provides visual information to the user ofthe computer system 10, indicating in which of the various powered-downstates the computer system currently operates. This contrasts withcurrently available computer systems in which the blinking LED signaldoes not distinguish between the various powered-down states. Of course,if a flashing LED is not deemed too unaesthetic, distinguishing thevarious powered-down states can be accomplished by correspondinglyvarying the flashing frequency, number, or pattern. Similarly, ifdistinguishing the various powered-down states is not desired, the moreaesthetic gradual variation in LED intensity of a set frequency can beemployed to indicate any of the powered-down states.

In the preferred embodiment of the present invention, the LED 46receives a pulsed current corresponding to a pulsed LED control signalproduced by the LED driver 44 and applied to the control terminal of thetransistor 48. Although a pulsed current is applied to the LED 46, thefrequency of the pulses is sufficiently high that a user viewing the LEDperceives a continuous optical signal output. The pulsed LED controlsignal has an adjustable duty cycle (as described below) to provide thevariable intensity optical output signal produced by the LED 46.

FIG. 3 depicts a first embodiment of the LED driver 44, which includes amicrocontroller 51, such as a PIC microcontroller from MicroChipTechnology, Inc. The microcontroller 51 has internal oscillatorcircuitry that generates a clock signal having a frequency determined bya crystal 53. Alternatively, the microcontroller 51 could receive aclock signal provided by (or derived from) the system clock. Themicrocontroller 51 also receives a plurality of MODE control signals,which are asserted by the system controller 16 of FIG. 1, eitherindividually or in combination as desired, to correspond with thevarious power-consumption states in which the computer system 10 canoperate. A duty register 52 stores a DUTY value provided by themicrocontroller 51. The duty register 52 provides the DUTY value to acomparator 54. A counter 56, such as a ring counter, receives a clockinput signal from the microcontroller 51 and produces an output COUNTvalue corresponding to a current count registered in the counter. Thecounter 56 provides the COUNT value to the comparator 54 which comparesthe COUNT value with the DUTY value stored in the duty register 52. Thecomparator 54 then produces the LED control signal, which has a highstate or a low state depending upon the relative magnitudes of the COUNTand DUTY values.

In operation, when the COUNT value of the counter 56 exceeds the DUTYvalue provided by the duty register 52, the comparator 54 generates alow state signal. When the DUTY value is greater than or equal to theCOUNT value, the comparator 54 produces a high state signal. In thisway, the comparator 54 generates the pulsed LED control signal having aduty cycle corresponding to the DUTY value stored in the duty register52. The transistor 48 functions as a switch, pulling current through theLED 46 when the LED control signal is in the high state and blockingcurrent when the LED control signal is in the low state. By regularvariation of the DUTY value stored in the duty register 52, the dutycycle of the LED control signal produced by the comparator 54 isadjusted, and the apparent intensity of the LED 46 varies accordingly.

FIG. 4 depicts a software routine 60 which is executable by themicrocontroller 51 of FIG. 3 to adjust the data values stored in theduty register 52. The software routine 60 is preferably stored in themicrocontroller's read only memory (ROM). When one of the system modetimers 40 expires, the computer system 10 of FIG. 1 is placed in acorresponding powered-down state in a conventional manner. The systemcontroller 16 asserts the MODE control signals to initiate execution ofthe software routine 60 in step 62. In step 64, a value TCONST is set toa value N, which is selected from a set of predetermined values storedin the microcontroller 51. The particular selected value N correspondsto the powered-down state in which the computer system 10 has beenplaced. Also in step 64, an incremental value VAL is set to 1. In step66, operation of the software routine 60 is paused for a time intervalcorresponding to the value TCONST. In step 68, the DUTY value stored inthe duty register 52 of FIG. 2 is incremented according to theincremented value VAL.

A conditional branch step 70 is executed in which the DUTY value iscompared to a maximum value MAX, which is a predetermined value storedin the microcontroller 51. If the DUTY value corresponds to the MAXvalue, the increment value VAL is set to -1, in step 72, and thesoftware routine 60 is routed to a conditional branch step 74. If,however, the DUTY value does not correspond to the MAX value, aconditional branch step 76 is executed in which the DUTY value iscompared to a MIN value, which is also a predetermined value stored inthe microcontroller 51. If the DUTY value corresponds with the MINvalue, the increment value VAL is set to 1 in step 78, and the softwareroutine 60 proceeds to the conditional branch step 74. If the DUTY valuedoes not correspond with the MIN value, the conditional branch step 74is executed in which it is determined whether the MODE control signalsreceived by the microcontroller 51 indicate that the power-consumptionstate of system operation has changed. If not, the software routine 60loops back to step 66 and the DUTY value is again incremented followingthe selected pause interval. If, however, the power-consumption state ofsystem operation has changed, the conditional branch step 74 routes thesoftware routine 60 to a sequence of operations 79 associated with thenew power-consumption state. If the new power-consumption state isanother of the powered-down states, the sequence of operations 79 isagain the software routine 60 with TCONST set to a corresponding newvalue N.

The frequency of variation of the apparent intensity of the LED 46 iscontrolled by the value N to which TCONST is set. Alternatively, thoseskilled in the art will appreciate that the incremental value VAL can beset to various selected magnitudes greater than 1 to achieve a similareffect. However, this alternative method requires a larger capacity dutyregister 52, and is therefore not preferred. Those skilled in the artwill also appreciate that software routine 60 may be executed by themicroprocessor 12 of FIG. 1, and that the microcontroller 51 of FIG. 3could be omitted from the computer system 10. In such an implementation,the software routine 60 is stored in a reserved system management memoryportion of the system DRAM 20, and is executed by the microprocessor 12in a system management mode, as is well-known in the art. However, thisimplementation is not preferred, because of the frequent systemmanagement interrupts (SMIs) required to continuously adjust the DUTYvalue.

Those skilled in the art will appreciate that one or more of thefunctions provided by the duty register 52, comparator 54, and thecounter 56 of FIG. 3 can themselves be integrated within a suitablemicrocontroller.

FIG. 5 depicts a second and preferred embodiment of the LED driver 44 ofFIG. 2. A microcontroller 80 has internal oscillator circuitry thatgenerates a clock signal having a frequency determined by a crystal 82.Alternatively, the microcontroller 50 could receive a clock signalprovided by (or derived from) the system clock. The microcontroller 80also receives a plurality of MODE control signals, which are asserted bythe system controller 16 of FIG. 1 to correspond with the variouspower-consumption states in which the computer system 10 can operate.The microcontroller 80 could be any of a wide variety of suitablemicrocontrollers, such as an Intel® or compatible 80C51SLmicrocontroller. A designer of the computer system 10 couldadvantageously combine the operations of the microcontroller 80 and thekeyboard/mouse controller 29 into a single microcontroller. Also, anumber of microcontrollers include high current output drivers, whichwould dispense with the need for the transistor 48 of FIG. 2.

The microcontroller 80 is programmed to receive the MODE control signalsand to produce the LED control signal having the characteristicsdescribed above in connection with the first embodiment of the LEDdriver 44. The duty cycle of the LED control signal is selectedaccording to the MODE control signal values. For example, when thecomputer system operates in a Full-On state, the duty cycle of theoutput signal produced by the microcontroller 80 causes the LED 46 ofFIG. 2 to produce a constant, high apparent intensity optical signal.When the computer system operates in a first powered-down state, the LEDcontrol signal produced by the microcontroller has a first modulatedduty cycle to cause the LED 46 to produce a first variable intensitysignal. When the computer system operates in a second powered-downstate, the microcontroller 80 produces the LED control signal with asecond modulated duty cycle which causes the LED 46 to produce a secondvariable optical output signal. The first and second modulationfrequencies are selected according to the respective powered-downstates. Those skilled in the art understand that any of a number ofconventional microcontrollers can be programmed to function asdescribed.

For example, the microcontroller 80 can execute a software routine whichis essentially the software routine 60 depicted in FIG. 4 and describedin connection with operations performed by the microcontroller 51 ofFIG. 3. However, in place of step 66 of FIG. 4, the microcontroller 80executes a software subroutine 100 which is depicted in FIG. 6. In step102, the value TCONST is decremented. A conditional branch step 104 isexecuted in which the value TCONST is compared to zero. If the valueTCONST is zero, the subroutine 100 is complete, and the software routine60 of FIG. 4 is rejoined at step 68. If, however, the value TCONST isnon-zero, a parameter D is set equal to the MAX duty value in step 106.The parameter D is then decremented in step 108, and the subroutine 100is routed to a conditional branch step 110, in which the parameter D iscompared to the DUTY value. If the parameter D does not exceed the DUTYvalue, the microcontroller 80 asserts the LED control signal to turn onthe LED 46 in step 112. If, however, the parameter D exceeds the DUTYvalue, the microcontroller 80 deasserts the LED control signal to turnoff the LED 6 in step 114. The parameter D is then compared to zero in aconditional branch step 116. If the parameter D equals zero, executionof the subroutine 100 begins again at step 102. If, however, theparameter D is non-zero, the conditional branch step 116 routes thesubroutine 100 back to step 108, in which the parameter D is againdecremented.

Programmable microcontrollers provide the circuit designer with aconvenient and flexible means of duplicating the function of variouscircuits. Those skilled in the art will appreciate that a number of purehardware circuits may be readily designed to function as the LED driver44 described in connection with FIG. 2. FIG. 7 depicts such anembodiment. A line select circuit 84, such as an LS139 series chip,receives a multibit MODE LEVEL input from the system controller 16 ofFIG. 1 and selectively asserts corresponding output line signals. A ringcounter 86 receives a TIME BASE signal and cyclically counts to 8 or to64, as determined by receipt of an asserted DIV8 or DIV64 controlsignal, respectively, provided by the line select circuit 84. AnOVERFLOW bit of the ring counter 86 is used as the time base for anup/down counter 88, which is reset by an asserted RESET control signalprovided by the line select circuit 84. Hence the up/down counter 88receives a different time base frequency, dependent on the cycle countof the ring counter 86. The up/down counter 88 provides a U/D-COUNTvalue corresponding to the current count registered in the up/downcounter. A digital-to-analog (D/A) converter 90 converts the digitalU/D-COUNT value into a corresponding magnitude analog LED control signalto control the current flow through the LED 46 of FIG. 2. Thus, themultibit MODE LEVEL input controls the rate at which the up/down counter88 counts, and hence the frequency of the LED control signal controllingthe magnitude of the optical signal produced by the LED 46. Thoseskilled in the art will appreciate that any number of readily designedcircuits may be functionally substituted for those shown in FIG. 7.

Each of the circuits whose function and interconnection is describedabove in connection with FIGS. 3, 5, and 7 are of a type known in theart, and one skilled in the art would be able to use such circuits inthe described combination to practice the present invention. Also, otherthan the system status indicator 42 (which is described in detail inconnection with FIGS. 2, 3, 5 and 7), each of the circuits whosefunction and interconnection is described above in connection with FIG.1 are of a type known in the art, and one skilled in the art would beable to use such circuits in the described combination to practice thepresent invention. The internal details of these particular circuits arenot part of, nor critical to, the invention, and a detailed descriptionof the internal circuit operation need not be provided. Similarly, thoseskilled in the art will appreciate that many of the individual stepsdepicted in FIGS. 4 and 6 and described above are, in fact, each asequence of operations which are well known in the art. One skilled inthe art would be able to program such operations in the describedsequence to practice the present invention. The various operationsassociated with each of the steps depicted in FIGS. 4 and 6 are not partof, nor critical to, the invention. Therefore, a detailed description ofthese operations is not required.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. For example, portions of the LEDdriver 44 could be advantageously integrated within the systemcontroller 16. Those skilled in the art will appreciate that numeroushardware embodiments are possible which function in a manner similar tovarious described embodiments of the LED driver 44. A number ofwell-known processor types, bus types, and system controller types couldbe employed according to the present invention. Additionally, variationson the sequence of operations described in connection with FIGS. 4 and 6are contemplated within the scope of the present invention. Accordingly,the invention is not limited except as by the appended claims.

I claim:
 1. A method of providing powered-down status information to auser of a computer system, comprising the steps of:determining a currentone of a plurality of powered-down states; selecting a corresponding oneof a plurality of system status signals, including selecting amodulation rate corresponding with the current powered-down state, eachof the selectable signal modulation rates corresponding one-to-one witha respective one of the powered-down states; and providing the selectedsystem status signal to the user by modulating the intensity of anoptical signal.
 2. In a computer system operable in a plurality ofpower-consumption states, a method of providing power-consumption statusinformation to a user of the computer system, comprising the stepsof:determining a current power-consumption state; and if the currentpower consumption state is a powered-down state, producing an apparentintensity optical signal which periodically varies gradually between agreatest intensity and a least intensity, wherein the step of producingan apparent intensity optical signal which periodically varies graduallybetween a greatest intensity and a least intensity includes the stepsof:selecting a duty cycle value; and applying a pulsed electric currenthaving the selected duty cycle value to a light-emitting diode.
 3. Themethod of claim 2 wherein the step of producing an apparent intensityoptical signal which periodically varies gradually between a greatestintensity and a least intensity includes the step of applying anelectric current to a light-emitting diode.
 4. The method of claim 2wherein the step of producing an apparent intensity optical signal whichperiodically varies gradually between a greatest intensity and a leastintensity further includes the steps of:after applying the pulsedelectric current having the selected duty cycle value to thelight-emitting diode for a selected time interval, modifying the dutycycle value; and applying a pulsed electric current having the modifiedduty cycle value to the light-emitting diode.
 5. The method of claim 2wherein the power-consumption states include On, first powered-down,second powered-down, and Off states, and wherein the step of producingan apparent intensity optical signal which periodically varies graduallybetween a greatest intensity and a least intensity includes the stepsof:varying the apparent intensity at a first rate if the currentpower-consumption state is the first powered-down state; and varying theapparent intensity at a second rate if the current power-consumptionstate is the second powered-down state.
 6. The method of claim 2 whereinthe least intensity is a non-zero intensity.
 7. In a computer systemoperable in a plurality of power-consumption states, a method ofcontrolling an optical signal produced by a light-emitting diode toprovide power-consumption status information to a user of the computersystem, comprising the steps of:selecting a duty cycle value; applying apulsed electric current having the selected duty cycle value to thelight-emitting diode; modifying the duty cycle value; and applying apulsed electric current having the modified duty cycle value to thelight-emitting diode; wherein the step of applying a pulsed electriccurrent having the selected duty cycle value to the light-emitting diodeis performed for a selected time interval prior to the step of modifyingthe duty cycle value.
 8. The method of claim 7 wherein the selected timeinterval is a first selected time interval corresponding with a firstone of a plurality of power-consumption states, and further comprisingthe step of selecting a second time interval corresponding with a secondone of the power-consumption states.
 9. In a computer system operable ina plurality of power-consumption states, a method of providingpower-consumption status information to a user of the computer system,comprising:determining in which of the power-consumption states thecomputer system presently operates; selecting one of a plurality ofsignal modulation rates, the selected signal modulation ratecorresponding with the present power-consumption state, and no twopower-consumption states having the same signal modulation rate; anddisplaying an optical signal having an intensity that varies inaccordance with the selected signal modulation rate.
 10. A methodaccording to claim 9 wherein:selecting one of a plurality of signalmodulation rates includes selecting a duty value and selectivelymodifying the duty value; and displaying an optical signal includesapplying a pulsed electric signal to a light source, the pulsed electricsignal having a duty cycle corresponding to the duty value.
 11. A methodaccording to claim 9 wherein at least one of the selectable modulationrates is zero.
 12. A method according to claim 9 wherein each of theselectable modulation rates corresponds one-to-one with a respective oneof the power-consumption states.
 13. In a computer system operable in aplurality of power-consumption states, a method of providingpower-consumption status information to a user of the computer system,comprising:determining in which of the power-consumption states thecomputer system operates; and producing one of a plurality of systemstatus signals, each corresponding with a respective one of thepower-consumption states, a first one of the system status signals beingan optical signal having an apparent intensity that varies graduallybetween a greatest and a least intensity; wherein a second one of thesystem status signals is an optical signal having an apparent intensitythat varies gradually between a greatest and a least intensity, theapparent intensity of the first and second system status signals varyingat first and second rates, respectively.
 14. A method according to claim13 wherein a third one of the system status signals is an optical signalhaving a substantially constant non-zero apparent intensity, and whereina fourth one of the system status signals is an optical signal having asubstantially constant zero apparent intensity.
 15. A method accordingto claim 14 wherein the power-consumption states include Full-On,Standby, Suspend, and Off states, the first and second system statussignals corresponding with the Standby and Suspend states, respectively,and the third and fourth system status signals corresponding with theFull-On and Off states, respectively.
 16. In a computer system operablein a plurality of power-consumption states, a method of controlling alight source to provide power-consumption status information to a userof the computer system, comprising:if the computer system operates in afirst of the power-consumption states, then applying a control signal tothe light source such that the apparent intensity of the light sourcevaries at a first rate; and if the computer system operates in a secondof the power-consumption states, then applying the control signal to thelight source such that the apparent intensity of the light source variesat a second rate.
 17. A method according to claim 16 wherein applyingthe control signal includes applying a pulsed electric signal having avariable duty cycle.
 18. A method according to claim 16 wherein:applyingthe control signal to vary the intensity at the first rate includesapplying a pulsed electric signal and varying the duty cycle of thepulsed electric signal at the first rate; and applying the controlsignal to vary the intensity at the second rate includes applying thepulsed electric signal and varying the duty cycle of the pulsed electricsignal at the second rate.